1. Field of the Invention
The present invention relates to a vibration isolator used suitably as, for example, an engine mount which vibroisolatingly supports an engine unit to be mounted on a vehicle.
2. Description of the Related Art
Conventionally, when an engine unit is mounted on a vehicle, such a vibration isolator as an engine mount is employed to support the engine unit vibroisolatingly, in order to suppress vibrations generated at the engine unit from being transmitted to a car body. An example of the conventional engine mount of this type is shown in FIGS. 11 to 13.
This engine mount comprises a cylindrical inner member 5; a mounting member 6 having a tubular portion 61 which is disposed outside of and at a distance from the inner member 5 approximately coaxially with the inner member 5, and two mounting seat portions 62, 63 which are integrally formed at an outer periphery of the tubular portion 61; a rubber elastic body 7 disposed between and connecting integrally the inner member 5 and the tubular portion 61, and having axially through cavity portions 71, 72; and an elastic stopper 8 projecting from an inner circumferential surface of the tubular portion 61 in a manner to face the inner member 5 by way of one cavity portion 71. At a portion of the tubular portion 61 where the elastic stopper 8 is formed, there are side stoppers 65, 65 extending in axially opposite directions and having the same thickness as the tubular portion 61. On the surface of each of the side stoppers 65, 65, there is disposed a thin portion 85 of the elastic stopper 8.
This engine mount is secured by fixing one of the inner member 5 and the mounting member 6 to an engine unit and fixing the other to a car body. In this case, the elastic stopper 8 is placed so as to stand in a main vibration input direction, and fore ends of brackets 55, 55 which are connected to both the ends of the inner member 5 are provided so as to face the side stoppers 65, 65.
When vibrations are input from the engine unit to the engine mount, the rubber elastic body 7 disposed between the inner member 5 and the tubular portion 61 of the mounting member 6 is deformed elastically, thereby damping the vibrations effectively. When relatively weak vibrations are input, the elastic stopper 8 is compressed by the inner member and the tubular portion 61, whereby relative displacement of the inner member 5 and the mounting member 6 is restricted elastically and vibration transmitting power is reduced effectively.
When strong vibrations are input, the fore ends of the brackets 55, 55 which are connected to both the ends of the inner member 5 come in contact with the thin portions 85, 85 of the elastic stopper 8 which are placed on the side stoppers 65, 65. Thus, excessive relative displacement of the inner member 5 and the mounting member 6 is restricted, and the rubber elastic body 7 and the elastic stopper 8 are prevented from being excessively deformed, so superior durability is secured.
By the way, the above conventional engine mount uses the brackets 55, 55 which are connected to both the ends of the inner member 5, and the side stoppers 65, 65 which extend in the axially opposite directions from the tubular portion 61 of the mounting member 6, as a stopper structure for restricting excessive relative displacement of the inner member 5 and the mounting member 6 when strong vibrations are input.
Because the side stoppers 65, 65 project axially, the tubular portion 61 of the mounting member 6 is increased in size. Besides, since the shape and size of the side stoppers 65, 65 must be determined in accordance with the shape and size of the brackets 55, 55 connected to the inner member 5, a lot of limitations are imposed on the design and the stopper structure becomes complicated.